Medical device for intraluminal endovascular stenting

ABSTRACT

A medical device includes a catheter and a stent mounted on the catheter, the stent having a hollow, cylindrical body made with a plurality of rings. The rings each extend circumferentially around the cylindrical body and include an undulating series of peaks and valleys. The rings are joined together by a series of links which are shaped and arranged to promote longitudinal flexibility as the stent is delivered on the catheter and effective scaffolding after deployment. In one aspect of the invention, the rings are provided with inflection points on some portions of the rings which extend in a generally circumferential direction for a short distance. A link is joined at one end at the inflection point on one ring and also joined at a second end at a second inflection point on an adjacent ring. This construction allows the crimped stent to flex longitudinally when it is subjected to bending forces such as those encountered during delivery of the stent and catheter through a tortuous coronary artery.

BACKGROUND OF THE INVENTION

This invention relates to intraluminal endovascular stenting, a methodby which a prosthesis is inserted into a body tube and expanded so as toreopen a collapsed vessel wall and prevent the wall from recollapsinginto the lumen. Endovascular stenting is particularly useful forarteries which are blocked or narrowed and is an alternative to surgicalprocedures that intend to bypass the occlusion.

Percutaneous transluminal coronary angioplasty (PTCA) is used to opencoronary arteries which have been occluded by a build-up of cholesterolfats or atherosclerotic plaque. Typically a guidewire is steered throughthe vascular system to the site of therapy. A guiding catheter, forexample, can then be advanced over the guidewire and a balloon catheteradvanced within the guiding catheter over the guidewire. The balloon atthe distal end of the catheter is inflated causing the site of thestenosis to widen. The dilatation of the occlusion, however, can formflaps, fissures and dissections which threaten re-closure of the dilatedvessel or even perforations in the vessel wall. Implantation of a metalstent can provide support for such flaps and dissections and therebyprevent reclosure of the vessel or provide a patch repair for aperforated vessel wall until corrective surgery can be performed.Reducing the possibility of restenosis after angioplasty reduces thelikelihood that a secondary angioplasty procedure or a surgical bypassoperation will be necessary.

An implanted prosthesis such as a stent can preclude additionalprocedures and maintain vascular patency by mechanically supportingdilated vessels to prevent vessel collapse. Stents can also be used torepair aneurysms, to support artificial vessels as liners of vessels orto repair dissections. Stents are suited to the treatment of any bodylumen, including the vas deferens, ducts of the gallbladder, prostategland, trachea, bronchus and liver. The body lumens range in size from1.5 mm in the coronary vessels to 30 mm in the aortic vessel.

A stent typically is a cylindrically shaped device formed from wire(s)ora tube and intended to act as a permanent prosthesis. A stent isdeployed in a body lumen from a radially compressed configuration into aradially expanded configuration which allows it to contact and support abody lumen. The stent can be made to be radially self-expanding orexpandable by the use of an expansion device. The self expanding stentis made from a resilient springy material while the device expandablestent is made from a material which is plastically deformable. Aplastically deformable stent can be implanted during an angioplastyprocedure by using a balloon catheter bearing a stent which has beencrimped onto the balloon. Stents radially expand as the balloon isinflated, forcing the stent into contact with the body lumen therebyforming a supporting relationship with the vessel walls. Deployment iseffected after the stent has been introduced percutaneously, transportedtransluminally and positioned at a desired location by means of theballoon catheter.

A balloon of appropriate size and pressure is first used to open thelesion. The process is repeated with a stent crimped on a balloon. Thestent is deployed when the balloon is inflated. The stent remains as apermanent scaffold after the balloon is withdrawn. A balloon capable ofwithstanding relatively high inflation pressures may be preferable forstent deployment because the stent must be forced against the artery'sinterior wall so that it will fully expand thereby precluding the endsof the stent from hanging down into the channel encouraging theformation of thrombus.

Previous structures used as stents or intraluminal vascular grafts haveincluded coiled stainless steel springs; helical wound spring coil madefrom shape memory alloy; expanding metal stents formed in a zig-zagpattern; diamond shaped, rectangular shaped, and other mesh and non-meshdesigns. Exemplary stent devices are disclosed in U.S. Pat. No.5,776,161 issued to Globerman, U.S. Pat. No. 5,449,373 issued toPinchasik et al, U.S. Pat. No. 5,643,312 issued to Fischell et al andU.S. Pat. No. 5,421,955 issued to Lau et al.

Problems to be overcome in stent design include inadequate radial forceto maintain expansion; inadequate scaffolding of tissue to the wall;pre-dilated longitudinal rigidity which negatively impacts on stentdelivery; and shortening of the stent as a consequence of radialexpansion. Predilation stent longitudinal rigidity is a significantshortcoming, and prevents the threading of the stent through longtortuous vessels and lesions. Shortening of the stent is also a problem,as it is important that the stent cover the entire lesion to minimizethe risk of post-operative complications. Many of these problems are theresult of difficult design problems resulting from the often conflictinggoals of stent design. For example, it is desirable to have a highdegree of scaffolding in the stent when the stent is expanded to itsrated radial size so that the vessel wall will have uniform support.However, it is also desirable to have a small, relatively smoothdelivered profile when the stent is mounted on the catheter to permitthe stent and catheter to traverse small diameter lesions. The personskilled in the art will appreciate that as a stent with a very smalldelivered profile expands radially its structural elements becomefarther apart and create openings which reduce the amount of scaffoldingavailable to support the vessel. A similar situation exists with respectto the conflicting goals of improved scaffolding and flexibility duringcatheter delivery since proper scaffolding will not be accomplished ifthere are few supporting structural elements and yet a stent with toomany structural elements may be difficult to crimp onto the ballooncatheter such that the structural elements will not abut or interferewith each other during delivery through tortuous vessels. Also, in somestents, during plastic deformation of the stent (i.e. balloon expansion)the strain is concentrated at small zones. This limits the properties ofthe material that can be used as well as the radial force and theexpansion rate.

U.S. Pat. No. 5,776,161 issued to Globerman, which is incorporated byreference herein in its entirety, addresses a number of these issues.Globerman discloses an expandable stent having a small initial diameter,flexibility along its longitudinal axis prior to expansion andminimization of rigid local strain on the stent material by the presenceof rotation joints which have minimal strain during stent expansion. Thestent is substantially the same length before and after expansion andbeing flexible longitudinally when constrained, it is easy to deliver.However additional improvements in longitudinal flexibility in thecrimped stent during delivery and scaffolding after delivery are stilldesired.

SUMMARY OF THE INVENTION

These and other objects are accomplished by the present invention. Themedical device of the present invention includes a catheter and a stentmounted on the catheter, the stent having a hollow, cylindrical bodymade with a plurality of rings. The rings each extend circumferentiallyaround the cylindrical body and include an undulating series of peaksand valleys. Typically, the undulating peaks and valleys of the ringsare formed by opposing curved segments joined to each other bysubstantially straight segments. The rings are joined together by aseries of links which are shaped and arranged to promote longitudinalflexibility as the stent is delivered on the catheter and effectivescaffolding after deployment and to prevent shortening of the stent asthe stent is expanded.

In one aspect of the invention, the rings are provided with inflectionpoints on some portions of the rings which extend between an adjacentpeak and valley of the ring. At each inflection point, a portion of thering extends in a generally circumferential direction for a shortdistance. Typically, the inflection point is substantially centeredbetween a peak and a valley of the ring. A link is joined at one end atthe inflection point on one ring and also joined at a second end at asecond inflection point on an adjacent ring. This link joins the ringstogether. Preferably, the link includes at least two curved segments inthe unexpanded device which are capable of deflecting to promote thetendency of the stent to flex longitudinally when it is subjected tobending forces such as those encountered during delivery of the stentand catheter through a tortuous coronary artery. Also preferably, theshort portion of the ring at the inflection point which extendsgenerally circumferentially has a length measured circumferentiallywhich is at least as great as the width of the link to which it isattached. Preferably, the circumferential length is no more than abouttwice the width of the link to which it is attached. This promotes thescaffolding provided to the vessel by the expanded stent since the linkscan be fit together closely in a nested arrangement with the undulationsof the rings as the stent is crimped on the balloon catheter. By “nest”,“nested” or nesting” herein we mean that the elements are conformallyarranged such they can be in very close proximity when the stent iscrimped onto the catheter but without substantial contact that wouldaffect the ability of the various elements to move in relation to eachother as the stent and catheter are advanced through a tortuous bodyvessel. Where the undulations of the ring include generally straightsegments between the peaks and valleys, the straight segments may beinterrupted by an inflection point which produces a offset portion inthe straight segment in a generally circumferential direction. In somepreferred embodiments of the invention, no more than one link isconnected to either of the first and second inflection points. Thismakes the inflection point a “dead end” in the longitudinal extent ofthe connecting links for the stent and permits some of the flexingforces which are not absorbed by the link itself to be absorbed by therings to which it is attached. The links can be arranged to provideflexibility whether the peaks and valleys of the rings are arranged tomake the rings appear to be mirror images to each other (i.e. peaks lineup with or closely approach each other) or whether the peaks and valleysare paired with each other in an in-phase relationship or any alignmentof the rings intermediate to those positions. Preferably, the rings arejoined by multiple links (most preferably 3 or more) and have the samenumber of inflection points on each ring as the number of attachinglinks. When a large number of connecting links are employed, any curvesor bends in the links are preferably of a complimentary shape to eachother such that they will nest together when the stent is crimped ontothe catheter.

Another aspect of the invention is the conformal nesting of ring andlink components such that the stent can be readily crimped onto aballoon or other expansion device on the catheter. The stent madeaccording to the present invention may be made from a tube which is cutwith lasers or other techniques which are well known to those skilled inthe art. The initial pattern cut into the tube includes link and ringcomponents which cooperate with each other but which provide sufficientspacing between components that the stent can be crimped onto a catheterwithout causing general abutment of the ring and link components witheach other and also permit longitudinal movement of the link componentswithout disturbing the crimp of the ring components on the catheterduring deployment of the stent through tortuous coronary arteries. Theneed for spacing between the components in the crimped condition must bebalanced with the need to provide improved scaffolding of the vesselbeing treated. A relatively abundant number of links provides improvedscaffolding of the vessel but potentially interferes with the ability tocrimp the stent onto the catheter. In the present invention, theinflection points can provide the spacing needed for the nesting of thering and link components by extending the ring in a generallycircumferential direction for a distance which is sufficient toaccommodate the width of the link component and provide space neededbetween the link components and the ring components which allows thestent to be crimped onto the catheter. In some embodiments of theinvention, each inflection point includes an attachment to twoconnecting links extending in opposing directions and thecircumferential offset at the inflection point provides for nesting ofboth connecting links with the ring components on the opposite sides.Thus, in the present invention, large numbers of connecting links can beincluded within a crimpable stent design.

Another aspect of the invention is to provide flexibility in the stentcrimped on the catheter such that the stent can flex near the inflectionpoints without significant radial expansion as the stent is subjected tobending along a longitudinal axis as it is advanced through bends in acoronary artery. As stents are advanced through tortuosities of avessel, they are subjected to bending forces which can producelongitudinal stresses on the connector links. If the movement ofconnector links pulls the undulations open from their crimped position,the stent can become radially enlarged and have difficulty in crossing anarrow lesion. The present invention reduces the potential for thisproblem by aligning the connection of the links with the rings at ashort, circumferentially extending portion, by providing curvature inthe links which are then able to flex and thereby reduce stress on thejunctions between the rings and the links and by providing “dead end”connections with the links which then avoids the transmission of forcesfrom ring to ring throughout the length of the stent.

Yet another aspect of the invention is in connection with the stentconfiguration in which the undulating peaks and valleys of the rings areoriented such that the rings have peaks and valleys which are pairedwith each other in an in-phase relationship. In such a configuration, alink can be provided which interconnects with the rings at points on therings which are substantially centered between the respective peaks andvalleys of the rings and yet allows the link to nest within the peaksand valleys of the rings. This can be accomplished by providing at leasttwo curved segments in the link in a central portion of the link.

Yet another aspect of the invention is in connection with the stentconfiguration in which the undulating peaks and valleys of the firstring are arranged with the undulating peaks and valleys of the secondring such that the first and second rings appear as mirror images ofeach other. In such a configuration, a link can be provided whichinterconnects with the rings at points on the rings which aresubstantially centered between the respective peaks and valleys of therings and yet allows the link to nest within the peaks and valleys ofthe rings. This can be accomplished by providing a link including asharp radius segment at each end and a gently curved central segment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view of a balloon catheter with a stent mountedon the balloon portion of the catheter.

FIGS. 2-5 are flattened plan views showing portions of stents madeaccording to the present invention. Each of the stent patterns shownwould be curved into a cylindrical shape as applied to the ballooncatheter as shown in FIG. 1.

FIGS. 5-14 are flattened plan views showing stents made according to thepresent invention. Each of the stent patterns shown would be curved intoa cylindrical shape as applied to the balloon catheter as shown in FIG.1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, the medical device 1 of the present inventionincludes a catheter 2 and a stent 3 mounted on the catheter 2 in anunexpanded condition. The stent 3 has a hollow, cylindrical body madewith a plurality of rings. As shown, the stent 3 is crimped over aballoon 4 affixed to the catheter 2 near the distal end of the catheter2. The stent 3 can include a variety of configurations as shown in FIGS.2 to 14 which are shown in an open and flattened configuration as theywould appear in an unexpanded and uncrimped condition. The balloon 4 canbe practically any balloon suitable for angioplasty procedures andcapable of inflation to 8 atmospheres of pressure. A preferred type ofballoon 4 is a balloon with multiple folds which permits the stent toexpand evenly that is approximately the same length as the stent. Inaddition to crimping, the stent 3 can be held onto the balloon 4 byretention techniques that are well known to those skilled in the art.

Referring now also to FIG. 2, rings 10 a-c are shown. Each of the rings10 a-c extend circumferentially around the cylindrical body of the stent3 and include an undulating series of peaks 11 and valleys 12. Theundulating peaks 11 and valleys 12 of the rings 10 a-c are formed byopposing curved segments 13 a-b joined to each other by substantiallystraight segments 14. The rings 10 a-c are joined together in arepeating pattern by a series of links 15 which are shaped and arrangedto promote longitudinal flexibility as the stent is delivered on thecatheter and effective scaffolding after deployment. In connection withthe stent 3 configuration of FIG. 2, it should be noted that theconfiguration of undulating peaks 11 and valleys 12 of the rings 10 a-care oriented such that the rings have peaks 11 and valleys 12 which arepaired with each other in an in-phase relationship. In thisconfiguration, a link 15 can be provided which interconnects with therings 10 a-c at points 16 a-b on the rings 10 a-b which aresubstantially centered between the respective peaks 11 and valleys 12 ofthe rings 10 a-c and yet allows the link to nest within the peaks 11 andvalleys 12 of the rings 10 a-c as the stent is crimped onto the balloon4 of the catheter 3. This is accomplished in part by providing at leasttwo curved segments 17 a-b in the link in a central portion of the link15. As shown in FIG. 2, no more than one link 15 is connected to eitherof the points 16 a-b. This makes the points 16 a-b “dead ends” in thelongitudinal extent of the connecting links 15 for the stent 3 andpermits some of the flexing forces which are not absorbed by the link 15itself at the curved segments 17 a-b to be absorbed by the rings 10 a-cto which it is attached. The nesting of link 15 and ring 10 a-ccomponents is also made possible by providing only three of the links 15attaching each of the rings 10 a-c to its immediate neighbor. Thisleaves some of the straight segments 14 without connections and thelinks are spaced-apart such that no links 15 have adjacent connectionsto the rings 10 a-c which oppose each other. A radiopaque marker 18 isjoined to ring 10 a inside a circular land portion 19 a link 15 a joinsthe land portion with the adjacent ring 10 b such that the link 15 aresides between two peaks of ring 10 a such that it will not interferewith the ring as the stent 3 is crimped onto the balloon 4 of thecatheter 2.

Referring now to FIGS. 1 and 3, in another embodiment of the invention,the rings 20 a-c are provided with inflection points 21 on some portionsof the rings 20 a-c which extend between an adjacent peak 22 and valley23 of the rings 20 a-c. At each inflection point 21, a portion of thering extends in a generally circumferential direction (indicatedgenerally 24) for a short distance. The inflection point 21 is shownsubstantially centered between a peak 22 and a valley 23 of the rings 20a-c. A link 25 is joined at one end at the inflection point 21 a on onering 20 a and also joined at a second end at a second inflection point21 b on an adjacent ring 20 b. This link 25 joins the rings 20 a-btogether. Each link 25 includes at least two curved segments 26 a-b inthe unexpanded stent 3 which promote the tendency of the stent 3 to flexlongitudinally when it is subjected to bending forces such as thoseencountered during delivery of the stent 3 and catheter 2 through atortuous coronary artery. It can be seen in FIG. 3 that the shortportion of the rings 20 a-c at the inflection point 21 which extendsgenerally circumferentially has a length measured circumferentiallywhich is about equal to a width of the link 25 to which it is attached.This promotes the scaffolding provided to the vessel by the expandedstent 3 since the links 25 can be fit together closely in a nestedarrangement with the undulations of the rings 20 a-c as the stent 3 iscrimped on the balloon 4 of the catheter 2. When as shown in FIG. 3, theundulations of the rings 20 a-c include generally straight segments 27between the peaks 22 and valleys 23, the straight segments 27 areinterrupted by an inflection point 21 which produces a offset portion inthe straight segment 27 in a generally circumferential direction 24.Only one link 25 is shown to be connected to either of the inflectionpoints 21 a-b. This makes the inflection point 21 a “dead end” in thelongitudinal extent of the connecting links 25 for the stent 3 andpermits some of the flexing forces which are not absorbed by the link 25itself to be absorbed by the rings 10 a-c to which it is attached. Thelinks 25 can be arranged to provide flexibility whether the peaks 22 andvalleys 23 of the rings 20 a-c are arranged to make the rings 20 a-cappear to be mirror images to each other (i.e. peaks line up with orclosely approach each other) or as shown here where the peaks 22 andvalleys 23 are paired with each other in an in-phase relationship or anyalignment of the rings intermediate to those positions. The rings 20 a-care joined by multiple links 25 (preferably 3 or more to provide goodscaffolding) and are shown to have the same number of inflection points21 on each ring 20 a-c as the number of attaching links 25. When a largenumber of connecting links 25 are employed, any curves or bends in thelinks 25 are preferably of a complimentary shape to each other such thatthey will nest together when the stent 3 is crimped onto the balloon 4of the catheter 2. It should also be noted in FIG. 3 that the end ring20 a includes a radiopaque marker 28 which provides fluoroscopicconfirmation of the position of the stent 3 when it is advanced into thepatient. The adjacent ring portions are provided with curved segments 29a-b which permit them to nest with the circular form of the marker 28 asthe stent 3 is crimped onto the balloon 4 of the catheter 2.

Referring now to FIGS. 1 and 4, in yet another embodiment of theinvention, the rings 30 a-c of the stent 3 have undulating peaks 31 andvalleys 32 arranged with the undulating peaks 31 and valleys 32 of anadjacent rings 30 a-c such that the rings 30 a-c appear as mirror imagesof each other. In such a configuration, a link 33 can be provided whichinterconnects with the rings 30 a-c at points on the rings which aresubstantially centered between the respective peaks 31 and valleys 32 ofthe rings 30 a-c and yet allows the link 33 to nest within the peaks 31and valleys 32 of the rings. This can be accomplished by providing alink 33 which includes a sharply curved segment 34 a-b at each end and astraight or gently curved central segment provided that it is connectedat a “dead end” where only one link 33 is connected at any one ringsegment between a peak 31 and valley 32. As shown, such a link 33 canalso nest with the opposing ring segments as the stent 3 is crimped ontothe balloon 4 of a catheter 2. Also shown in FIG. 4 is the adjustment inthe relative amplitudes of the undulations between the rings 30 a-c.Ring 30 a is shown to have a smaller amplitude in dimension “A” than theamplitude of ring 30 b as shown in dimension “B”. This variation inamplitude can be particularly important in stent designs where the stent3 may tend to flare at the ends as the stent is advanced throughtortuous arteries since the lower amplitude ring 30 a at the end of thestent 3 will have a reduced tendency to be deformed and tip outward whenthe stent 3 is subjected to longitudinal bending forces. The loweramplitude ring 30 a can be on a distal or proximal end of the stent 3.The person skilled in the art will appreciate that this can beespecially important in situations where one advances the stent 3 andcatheter 2 through a tortuous artery but, instead of deploying the stent3, then wishes to withdraw the stent 3 into the guide catheter while itis still crimped on the balloon 4. If the end of the stent 3 has becomeflared during the failed deployment, it can catch on the distal edge ofthe guide catheter as it is being withdrawn.

Referring now to FIGS. 1 and 5, a full pattern of a stent 3 for acoronary artery application is shown which is substantially the samepattern which was discussed above in connection with FIG. 3. The stent 3has a length “A” which can be about 8 to 30 mm (and as depicted could beabout 15-25) mm for a coronary artery application although those skilledin the art will appreciate that the pattern can be configured to givemany lengths. The dimension “B” refers to the circumference of the stent3 for a coronary application which can be about 3-7 mm and gives anuncrimped diameter for the stent 3 of about 1-2 mm. The dimension “C”refers to the width of one of the rings which in this example could bein the range of about 0.08 to 0.12 mm. The dimension “D” refers to theamplitude of one of the rings and in this example could be in the rangeof about 0.75 to 2.5 mm. The dimension “E” refers to the peak-to-peakspacing for the rings and in this example could be in the range of about1-3 mm. The dimension “F” refers to the width of a connecting link andin this example could be in the range of about 0.06 to 0.1 mm. Thedimensions G and H refer to the diameter of the radiopaque marker andthe width of the portion of the ring holding the marker. This stent 3can be made by laser cutting from a tube of stainless steel or othersuitable material by methods which are well known by those skilled inthe art. Similar structures are marked with the same dimensional symbols(“A” to “H”) in each of the drawings FIGS. 5-14 for the convenience ofthe reader.

Referring now to FIG. 6, the stent 3 of FIG. 5 has been modified by theaddition of more connecting links 40 and the use of shorter amplituderings 41 (i.e. reductions in dimensions “D” and “E”) in combination withreductions in the widths in various components (i.e. reductions indimensions “C” and “F”) in order to provide better crimp profile,flexibility and scaffolding. It should be noted in connection with FIG.6 and other drawing figures that the links 40 can vary somewhat in widthalong their length in order to modify or direct the way in which thelink 40 can flex as the stent 3 is deployed through a tortuous bodylumen. In this embodiment of the stent 3, the ends of the links 40 flareout just before the connection points 42 a-b in order to provideincreased resistance to flexing near the connection points 42 a-b.

Referring now to FIG. 7, the stent 3 is made in a configuration whichcombines features shown in the stents 3 of FIGS. 3 and 4. The stent 3employs rings 50 which are arranged in a mirror image configuration.Connecting links 51 are connected to rings 50 at inflection points 52a-b with a slightly curved connecting link 51 which provides improvedflexibility. The connecting links 51 “dead end” at the inflection points52 a-b to also provide flexibility. The number of rings 50 are increasedand the amplitude of the rings 50 is reduced (i.e. reductions indimensions “D”, “E”, “C” and “F”). Thus the “cell” size ( i.e. the sizeof the smallest repeating unit in the pattern) is reduced andscaffolding is improved.

Referring now to FIG. 8, the stent 3 of FIG. 6 is modified by adding alonger and more highly curved link 60 and by adding another two bends inthe undulation in each of the rings 61. The resulting stent 3 hadimproved scaffolding from smaller cell size and more flexibility fromthe more curved link 60. Radiopaque markers 62 a-b nest with theadjacent ring elements as the stent 3 is crimped onto the balloon 4 ofthe catheter 2. In addition, the links 60 a-b connecting the ringimmediately adjacent to the radiopaque markers are shorter than theother links and are attached to the ring at a portion of the ring awayfrom the radiopaque marker 62 a. This provides the markers 62 a-b withadditional space and ring flexibility to permit improved crimping of thestent 3 onto the balloon 4.

Referring now to FIG. 9, the stent 3 is a maximum flexibility version ofthe stent 3 of FIG. 8 made by making the connecting link 70 even morecurved and increasing the cell size to permit the link 70 to flex in thespace between the peaks 71 and valleys 72 of adjacent rings 73.

Referring now to FIG. 10, the stent 3 is a variant of the stent 3 ofFIG. 6 in which the dimension “D” is relatively smaller in relation todimension “E” such that more space is available between the rings 80 sothat the stent 3 can flex with maximum clearance between thosecomponents when the stent 3 is deployed in the bend of a body lumen.Radiopaque markers 82 a-b are located at opposite ends of the stent 3 toallow the physician to precisely identify the position of the ends ofthe stent 3 fluoroscopically while the stent 3 is being deployed intothe patient. The markers 82 a-b can take the form of a thin gold diskset into an portion of the pattern. The markers 82 a-b have theirhighest fluoroscopic visibility when looking directly down onto the flatplane of the disk and lesser visibility when looking at the edge of thedisk. Therefore, the markers 82 a-b can be aligned with each other so asto both be visible at the same intensity no matter what the rotationalorientation of the stent (as shown in FIG. 9) or offset (shown in FIG.10 about 90 degrees offset) with regard to each other to permit at leastone marker 82 a-b to always be viewed in its highly observable flatorientation. More markers can be added to those shown in FIGS. 9-10 sothat each end of the stent 3 has two or more markers in a relativeoffset position which then permits one of the markers at each end toalways be brightly observable no matter what rotational orientation thestent 3 is in.

Referring now to FIG. 11, the stent 3 is a variant of the stent 3 ofFIGS. 3 and 4 with long, relatively straight links 90 joined with rings91 at inflection points 92 a-b. It should be noted that in the center ofthe pattern two links 90 are joined at each inflection point 92 a-b onopposing sides without compromising the ability of the ring 91 and link90 elements to nest as the stent 3 is crimped onto the balloon 4 of thecatheter 2. The use of multiple links 90 at each inflection point 92 a-bprovides a greater number of links 90 overall and a therefore a greateramount of scaffolding in the expanded stent 3 than in other designs.

Referring now to FIG. 12, the stent 3 is a variant of the stent 3 ofFIGS. 3 and 12 with curved connecting links 100 replacing the straighterlinks in FIG. 12. Again, the links 100 are connected to the rings 101 atinflection points 102 a-b such that more than one link 100 is attachedat each inflection point 102 a-b.

Referring now to FIG. 13, the stent 3 is a variant of the stent 3 ofFIG. 12 in which a longer and more curved link 110 is used to improveflexibility of the stent 3. The links 110 include a peaked portion 111which extends in the circumferential direction of the stent 3. It isimportant to note that the links 110 have peaked portions which have theability to conform to each other and nest as the stent 3 is crimped ontothe balloon 4 of the catheter 2.

Referring now to FIG. 14, the stent 3 is a variant of the stent 3 ofFIG. 13 in which the cell size is increased slightly and the shape ofthe peaked portion 120 a-b of each link 121 are altered so that theadjacent peak portions 120 a-b will conform and nest better when thestent 3 is crimped. It will be noted that every peak portion 120 a-b isslightly offset from its nearest neighbor to compensate for the slightalteration in the shape of the link 121 that takes place as the stent 3is crimped. This provides a more precise nesting of the links 121 in thecrimped stent 3. Also to be noted in connection with FIG. 14 is therelative position of the connecting links 121, 122 with respect to theinflection point 123 a. The first connecting link 121 is connected tothe inflection point 123 a at a lower portion of the inflection point123 a while the second connecting link 122 is connected at an oppositeside of the inflection point 123 a at an upper portion of the inflectionpoint 123 a. With the in-phase arrangement of peaks 124 and valleys 125in this pattern, the connecting links 121, 122 are connected to adjacentrings 126 a-b such that a link 121 connects at one end to one ring 126 aat a lower portion of the inflection point 123 a and at the other end atan upper portion of the inflection point 123 b. Also to be noted in thepattern of FIG. 14 is that each peak 124 and each valley 125 has twoconnecting links 121, 122 extending laterally past them to join withanother ring 126 a-b. The connecting links 121, 122 proceed from one endattachment at an inflection point 123 a-b such that they parallel theportion of the ring 126 a-b and are positioned such that when the stent3 is expanded they will extend outward from the inflection point 123 a-band assist in the scaffolding provided by the central portion of thering 126 a-b. The connecting links 121, 122 also extend past the peak124 or valley 125 components to extend the scaffolding provided by thepeak 124 and valley 125 components of the rings 126 a-b toward the nextring. In particular, the connecting links 121, 122 extend upwardly pastthe peak 124 and valley 125 portions of the rings 126 a-b into peakedportions 120 a-b. This arrangement provides highly effective scaffoldingfor the stent 3 when it is expanded against a body lumen of the patient.

Those skilled in the art will further appreciate that the presentinvention may be embodied in other specific forms without departing fromthe spirit or central attributes thereof. In that the foregoingdescription of the present invention discloses only exemplaryembodiments thereof, it is to be understood that other variations arerecognized as being within the scope of the present invention.Accordingly, the present invention is not limited to the particularembodiments which have been described in detail herein.

We claim:
 1. A medical device comprising: a catheter and a stent mountedon the catheter, the stent comprising a hollow, cylindrical bodycomprised of a first ring and a second ring, the first and the secondrings each extending circumferentially around the cylindrical body, thefirst and second rings each including an undulating series of peaks andvalleys; a first inflection point on the first ring, the firstinflection point disposed on an intermediate portion of the first ringsubstantially centered between an adjacent peak and valley, the firstinflection point including a portion extending generallycircumferentially; a second inflection point on the second ring, thesecond inflection point disposed on an intermediate portion of thesecond ring substantially centered between an adjacent peak and valley,the second inflection point including a portion extending generallycircumferentially; a link joined at a first end at the first inflectionpoint on the first ring and at a second end at the second inflectionpoint whereby the first and second rings are joined together.
 2. Amedical device as in claim 1 wherein the link includes at least twocurved segments.
 3. A medical device as in claim 1 wherein the portionof the inflection point extending generally circumferentially has alength measured circumferentially which is substantially equal to awidth of the link to which it is attached.
 4. A medical device as inclaim 1 wherein the stent is crimped onto a distal portion of thecatheter.
 5. A medical device as in claim 4 wherein a portion of thelink near its first end nests within the undulating series of peak andvalleys of the first ring of the crimped stent.
 6. A medical device asin claim 4 wherein the crimped stent can flex near the first and secondinflection points without significant radial expansion as the stent issubjected to bending along a longitudinal axis as it is advanced throughbends in a coronary artery.
 7. A medical device as in claim 1 whereinthe undulating peaks and valleys of each of the first and second ringsare formed by opposing curved segments joined to each other by straightsegments.
 8. A medical device as in claim 7 wherein at least one of thestraight segments is interrupted by an inflection point which produces agenerally circumferentially offset portion in the straight segment.
 9. Amedical device as in claim 1 wherein no more than one link is connectedto either of the first and second inflection points.
 10. A medicaldevice as in claim 1 wherein the undulating peaks and valleys of thefirst ring are arranged with the undulating peaks and valleys of thesecond ring such that the first and second rings appear as mirror imagesof each other.
 11. A medical device as in claim 1 wherein the undulatingpeaks and valleys the first ring are arranged with the undulating peaksand valleys of the second ring such that the first and second rings havepeaks and valleys which are paired with each other in an in-phaserelationship.
 12. A medical device as in claim 1 wherein the first andsecond rings each include the same number of inflection points.
 13. Amedical device as in claim 1 wherein the first and second rings arejoined by a plurality of links.
 14. A medical device as in claim 13wherein the plurality of links have complimentary shapes such that theywill nest when the stent is crimped onto the catheter.
 15. A medicaldevice comprising: a catheter and a stent mounted on the catheter, thestent comprising a hollow, cylindrical body comprised of a first ringand a second ring, the first and the second rings each extendingcircumferentially around the cylindrical body, the first and secondrings each including an undulating series of peaks and valleys; a firstinflection point on the first ring, the first inflection point disposedon an intermediate portion of the first ring substantially centeredbetween an adjacent peak and valley; a second inflection point on thesecond ring, the second inflection point disposed on an intermediateportion of the second ring substantially centered between an adjacentpeak and valley; a link joined at a first end at the first inflectionpoint on the first ring and at a second end at the second inflectionpoint whereby the first and second rings are joined together; the stentcrimped on the catheter such that the link nests near the first endwithin the undulating series of peaks and valleys of the first ring andalso nests near the second end within the undulating series of peaks andvalleys of the second ring.
 16. A medical device as in claim 15 whereinthe link includes at least two curved segments.
 17. A medical device asin claim 15 wherein the inflection point has a length measuredcircumferentially which is substantially equal to a width of the link towhich it is attached.
 18. A medical device as in claim 15 wherein thecrimped stent can flex near the first and second inflection pointswithout significant radial expansion as the stent is subjected tobending along a longitudinal axis as it is advanced through bends in acoronary artery.
 19. A medical device as in claim 15 wherein theundulating peaks and valleys of each of the first and second rings areformed by opposing curved segments joined to each other by straightsegments.
 20. A medical device as in claim 19 wherein at least one ofthe straight segments is interrupted by an inflection point whichproduces a generally circumferentially offset portion in the straightsegment.
 21. A medical device as in claim 15 wherein no more than onelink is connected to either of the first and second inflection points.22. A medical device as in claim 15 wherein the undulating peaks andvalleys of the first ring are arranged with the undulating peaks andvalleys of the second ring such that the first and second rings appearas mirror images of each other.
 23. A medical device as in claim 15wherein the undulating peaks and valleys of the first ring are arrangedwith the undulating peaks and valleys of the second ring such that thefirst and second rings have peaks and valleys which are paired with eachother in an in-phase relationship.
 24. A medical device as in claim 15wherein the first and second rings each include the same number ofinflection points.
 25. A medical device as in claim 15 wherein the firstand second rings are joined by a plurality of links.
 26. A medicaldevice as in claim 25 wherein the plurality of links have complimentaryshapes such that they will nest when the stent is crimped onto thecatheter.
 27. A medical device comprising: a catheter and a stentmounted on the catheter, the stent composing a hollow, cylindrical bodycomprised of a first ring and a second ring, the first and the secondrings each extending circumferentially around the cylindrical body, thefirst and second rings each including an undulating series of peaks andvalleys; a first inflection point on the first ring, the firstinflection point disposed on a portion of the first ring substantiallycentered between an adjacent peak and valley; a second inflection pointon the second ring, the second inflection point disposed on a portion ofthe second ring substantially centered between an adjacent peak andvalley; a link joined at a first end at the first inflection point onthe first ring and at a second end at the second inflection pointwhereby the first and second rings are joined together; the stentcrimped on the catheter such that the stent can flex near the first andsecond inflection points without significant radial expansion as thestent is subjected to bending along a longitudinal axis as it isadvanced through bends in a coronary artery.
 28. A medical device as inclaim 27 wherein the link includes at least two curved segments.
 29. Amedical device as in claim 27 wherein the inflection point has a lengthmeasured circumferentially which is substantially equal to a width ofthe link to which it is attached.
 30. A medical device as in claim 27wherein the undulating peaks and valleys of each of the first and secondrings are formed by opposing curved segments joined to each other bystraight segments.
 31. A medical device as in claim 30 wherein at leastone of the straight segments is interrupted by an inflection point whichproduces a generally circumferentially offset portion in the straightsegment.
 32. A medical device as in claim 27 wherein no more than onelink is connected to either of the first and second inflection points.33. A medical device as in claim 27 wherein the undulating peaks andvalleys of the first ring are arranged with the undulating peaks andvalleys of the second ring such that the first and second rings appearas mirror images of each other.
 34. A medical device as in claim 27wherein the undulating peaks and valleys of the first ring are arrangedwith the undulating peaks and valleys of the second ring such that thefirst and second rings have peaks and valleys which are paired with eachother in an in-phase relationship.
 35. A medical device as in claim 27wherein the first and second rings each include the same number ofinflection points.
 36. A medical device as in claim 27 wherein the firstand second rings are joined by a plurality of links.
 37. A medicaldevice as in claim 36 wherein the plurality of links have complimentaryshapes such that they will nest when the stent is crimped onto thecatheter.
 38. A medical device comprising: a catheter and a stentmounted on the catheter, the stent comprising a hollow, cylindrical bodycomprised of at least one ring, the ring extending circumferentiallyaround the cylindrical body, the ring including an undulating series ofpeaks and valleys; an inflection point on the ring, the inflection pointdisposed on an intermediate portion of the ring substantially centeredbetween an adjacent peak and valley; a first link joined at an end atthe inflection point.
 39. A medical device as in claim 38 wherein theinflection point includes a short portion extending generallycircumferentially.
 40. A medical device as in claim 39 wherein the shortportion of the inflection point extending generally circumferentiallyhas a length measured circumferentially which is substantially equal toa width of the link.
 41. A medical device as in claim 38 wherein thelink extends substantially parallel to a portion of the ring.
 42. Amedical device as in claim 38 wherein the link extends beyond a peak orvalley of the ring.
 43. A medical device as in claim 38 also comprisinga second link joined at an end at the inflection point and extendingfrom the inflection point in a direction substantially opposite to thefirst link.
 44. A medical device as in claim 43 wherein the first linkis joined at an upper portion of the inflection point and the secondlink is joined at a lower portion of the inflection point.
 45. A medicaldevice as in claim 43 wherein the first link is joined to the ring abovethe ring and the second link is joined to the ring below the ring.
 46. Amedical device as in claim 38 wherein the stent is crimped onto a distalportion of the catheter.
 47. A medical device as in claim 46 wherein aportion of the link nests within the undulating series of peaks andvalleys of the ring of the crimped stent.
 48. A medical device as inclaim 46 wherein the crimped stent can flex near the inflection pointwithout significant radial expansion as the stent is subjected tobending along a longitudinal axis as it is advanced through bends in acoronary artery.
 49. A medical device as in claim 38 wherein theundulating peaks and valleys of the ring are formed by opposing curvedsegments joined to each other by straight segments.
 50. A medical deviceas in claim 49 wherein the inflection point forms an offset at at leastone of the straight segments to produce a generally circumferentiallyoffset portion in the straight segment.
 51. A medical device as in claim38 wherein the ring includes a plurality of inflection points and aplurality of links joined to the inflection points.
 52. A medical deviceas in claim 51 wherein each peak and valley has an inflection pointtherebetween and a first link joined at each inflection point.
 53. Amedical device as in claim 52 wherein each inflection point has a secondlink joined at each inflection point and extending longitudinallyopposite the first link.
 54. A medical device as in claim 52 wherein theplurality of links have complimentary shapes such that they will nestwhen the stent is crimped onto the catheter.
 55. A medical device as inclaim 38 wherein the link varies in width.
 56. A medical device as inclaim 55 wherein the link is wider at the end attached to the inflectionpoint.